The present invention relates in general to varying spatial characteristics and more particularly concerns novel apparatus and techniques for varying the spatial characteristics of a loudspeaker such as the BOSE 901 Series III loudspeaker which radiates predominantly more sound energy upon a reflecting surface first and then into a listening area than it radiates directly into the listening area to enable the listener to control the apparent sound image, thereby enhancing the listening experience with structure that is relatively free from complexity and easy to control.
The BOSE 901 loudspeaker system embodies the invention patented in U.S. Pat. No. 3,582,553 and has met with wide critical and consumer acclaim throughout the world, receiving an unprecedented series of rave reviews. The 901 system includes a pair of adjacent rear-facing angled panels filled with like in-phase-connected loudspeaker drivers operative over the full frequency range for radiating sound energy first upon a reflecting surface and then into the listening area with a single driver on the front panel for radiating significantly less sound energy directly into the listening area. An associated active equalizer coacts with the loudspeakers to provide a system characterized by a substantially uniform radiated power response as a function of frequency over substantially the entire audio frequency range.
This system simulates the sound received in a concert hall where the listener receives significantly more reflected energy than direct energy from the sound source on the stage. The listener perceives the relatively broad sound image as if the sound source originated from across the entire surface of the wall adjacent to the loudspeaker cabinets. Alteration of the sound energy may be effected by altering the angle between the panels and the adjacent wall. For example, the perceived image may be moved closer to the center by rotating the cabinet so that the angle between the outside rear panels and the facing wall is reduced while that between the inside rear panels and the facing wall is increased. Conversely, increasing the latter and reducing the former tends to move the perceived image further outward. While this physical movement provides some control of perceived image, it is impractical in many situations where the listener may want to alter the perceived image from selection to selection, especially where the loudspeakers are suspended from the ceiling. Furthermore, the degree of image alteration is somewhat limited.
Accordingly, it is an important object of this invention to provide improved methods and means for varying spatial characteristics of a loudspeaker by electrical means.
It is a further object of the invention to achieve the preceding object with a loudspeaker of the type of a BOSE 901 loudspeaker system.
It is a further object of the invention to achieve one or more of the preceding objects over a relatively wide range and with a single control that is easy to operate by a technically unskilled listener.
It is still a further object of the invention to achieve one or more of the preceding objects without altering the volume.
It is still a further object of the invention to achieve one or more of the preceding objects with the addition of relatively little additional apparatus that is reliable and relatively inexpensive.